1. Field of the Invention
The present invention relates to a bonding tool for ultrasonic bonding and a method of ultrasonic bonding, and in more detail to a bonding tool for ultrasonic bonding and a method of ultrasonic bonding that are used during assembly and the like of a carriage assembly that composes a magnetic disk apparatus.
2. Related Art
Ultrasonic bonding is widely used for bonding operations such as the flip-chip bonding of semiconductor chips and the bonding of inner leads of TAB tapes and electrodes. During ultrasonic bonding, it is important to reliably transmit ultrasonic vibration to the parts to be bonded using a bonding tool so that bonding can be carried out stably and reliably. To do so, research is being conducted into carrying out bonding with projections and/or roughened surface parts having been formed on the pressure welding part of an end surface of the bonding tool, which contacts the bonded object and applies ultrasound, so as to prevent slippage between the pressure welding part of the bonding tool and a contact surface of the bonded object (see Patent Documents 1 to 3).
Patent Document 1
Japanese Laid-Open Patent Publication No. H05-21541
Patent Document 2
Japanese Laid-Open Patent Publication No. H07-58155
Patent Document 3
Japanese Laid-Open Patent Publication No. 2000-315708
However, when ultrasonic bonding is repeatedly carried out using a bonding tool, abrasion occurs for the pressure welding part of the bonding tool and foreign matter adheres to the pressure welding part, so that the form of the pressure welding part of the bonding tool gradually changes from the initial state.
FIG. 7A shows the initial state of a pressure welding part of a bonding tool 10, and FIG. 7B shows the state after the bonding tool 10 has been used many times. Due to gold plating formed on surfaces of leads of the bonded object and/or a nickel or copper layer that is a base for the plating adhering to the pressure welding part of the bonding tool 10, the end surfaces of protrusions 12 become rounded as shown in FIG. 7B.
In this way, when the form of the pressure welding part of the bonding tool 10 changes, slipping occurs between the bonding tool 10 and the contact surface of the bonded object, so that there are the problems that ultrasonic vibration is no longer reliably transmitted from the bonding tool to the bonded object, the bonding strength of the bonds gradually falls from the initial state of the bonding tool 10, and a stabilized bonding strength can no longer be achieved.